Company sales manager Ken Hill described the system for International Longwall News as the key collaboration of its components that include a Network Controller (NC), single or multiple Sub-Net Controllers (SNCs), up to 75 Wireless Access Points (WAPs), and worker-donned Mobile Location Transponders (MLTs).
The NC is the brain of the system located at the surface in the mine's office to provide monitoring staff with visual illustrations of activity. The NC can also be linked to an operation's IT department for access from anywhere, Hill said.
The SNC will be connected to the NC via a looped data connection, and may be tethered by one or multiple points by a twisted pair RS 485 line resembling a telephone line.
"The loop provides multiple data paths should a break in the line occur, [and] the connection from the SNCs to the NC is the only wired communications link in the system," Hill said.
The WAPs distributed throughout the mine are the links that will provide information on location and serve as communications relays.
"If this were a cellular phone system the WAPs would be the cell towers," Hill explained, adding that they can be positioned up to a mile away from the SNC and in up to three directions or entries.
The WAPs also feature multi-coloured strobes for visual alerts to workers, such as a mandatory evacuation, and can be programmed so that all miners moving throughout the mine can be transported safely and efficiently.
"Should a portion of the system lose communications with the mine office, that portion will be illuminated such that only strobes between miners will be lit. This will facilitate miners locating one another," said Hill.
The MLTs, much like a cell phone and worn by miners, transport data between the workers and the surface via the WAP infrastructure. They provide the mine office with the identity of the person in motion as well as allow for two-way communications with them via text messaging.
"Since each MLT has a unique address, communications can be directed to an individual or broadcast to all if required," Hill said of the system's benefit for flexible communication.
"Since all of the communications are digital, every miner is assured of having all of his messages communicated to the mine office and all miners can be communicating simultaneously with no interruption of service.
"There is no potential for a single user to tie up or occupy the communications link such as can occur with voice radios."
He noted the need for redundancy with underground communications, an idea put on the front burner by the MINER Act of 2006. The underlying technology used in MineTracer is ZigBee-based mesh communications; inherent to that system's use are self-forming and self-healing path capabilities.
"In the case of a roof fall or other accident, if a communications link is broken, the system will seek the most efficient routing to re-establish communications with the mine office," explained Hill.
"Should a portion of the system lose communications with the mine office, it will continue to function with all other components in range until a link can be re-established."
If communications are lost with the surface, the system automatically works to "heal" its path and reconfigure itself. Those cut off from the path will then be connected to one another.
Hill noted much of the issue with redundancies, in his opinion, comes down to economics.
"What the redundancy is aiming to accomplish is to eliminate interruption of service, and primarily post incident, [which] can be accomplished with redundancy built into a single system or installation of multiple systems with divergent failure mechanisms," he said.
He said Helicomm is not opposed to the idea of doubling up on technology; the central issue is financially based and involves how many systems - and how much of a system - will provide a mine's needed coverage.
Communications are key whether occurring before or after an incident. If an occurrence can potentially be foreseen, such as the trigger of environmental monitors, the surface can tell underground staff of the situation, and those workers in turn can communicate with one another.
For communications to be effective post-accident, a mine must have a workable plan for emergency communications.
"NIOSH published a study in 1999 defining the emergency communications triangle," Hill pointed out.
"The beauty of our system is that we can provide all of the elements of the communications triangle simultaneously for all in the mine."
He added that those entering shafts and slopes to work a shift below ground each day know that their options for finding a safe location are limited in an emergency situation. The industry can further secure the confidence in communications by providing all available information and technology to mine rescue teams.
"Rather than using a shotgun approach to facilitate rescue, a laser guided effort will be much more efficient. MineTracer's location accuracy will give rescue teams the ability to triage before deploying resources," Hill said.
